The present invention relates to spray coating systems, and in particular to an electrostatic air atomization spray coating system having a hand held spray gun, wherein energization of a power supply for electrostatically charging spray particles may be controlled from the spray gun itself to selectively permit air atomization spraying with or without electrostatics.
In electrostatic air atomization spray coating systems, paint is applied to ware by means of a spray gun which atomizes the paint into a spray and includes a circuit which applies an electrostatic charge to the spray particles. Typically, the ware is grounded so that charged spray particles are attracted to and tend to uniformly cover all exposed areas of the ware. Electrostatic charging of the spray particles is usually accomplished by contacting the spray with an electrode as the spray is emitted, and to this end the electrode is maintained by a high voltage power supply at a voltage which may range from several thousand to 100,000 volts.
In conventional electrostatic air atomization spray coating systems using hand held spray guns, for reasons of safety it is desirable that the power supply be deenergized when spraying is not occurring, so that a high voltage is not then present at the charging electrode on the gun. It is also desirable that deenergization of the power supply occur automatically without overt action by an operator, so that each and every time spraying is terminated, voltage is removed from the electrode. To this end, the flow of atomizing air to the gun, which occurs when the gun is triggered on, is sensed by an air flow sensor for controlling energization of the power supply, the arrangement being such that when the gun is triggered on and a flow of air occurs, the power supply is energized, and when the gun is triggered off and the flow ceases, the power supply is deenergized. Such air flow sensors and their use in controlling power supplies in air atomization electrostatic spray coating systems are known in the art, and two representative sensors and systems employing the same are taught by Croskey et al U.S. Pat. No. 2,916,576 and Kozinski et al U.S. Pat. No. 3,864,603.
A disadvantage of systems of the foregoing type is that whenever the gun is triggered on, the power supply is energized. Consequently, when articles being painted have, for example, inside corners, it is difficult to perform final touch up work because of electrostatic charging of the spray, it being known that electrostatically charged spray particles are much more strongly attracted to side walls defining an inside corner, rather than into the corner itself. Usually, to perform such touch up work an operator must first turn off the power supply by means of a switch thereon, so that the power supply will not be energized when the gun is triggered on, which is inconvenient because he must leave the work area and walk over to the power supply to turn it off, and then return to the power supply to turn it back on when touch up is completed.